I think we’re reading the definitions kind of backwards. OK, runways more than 30degs offset (15degs for GPS) from the instrument FAT are designated as circling approaches but that is to stop you going down to the (normally) more permissive PA/NPA minima for the IA runway and trying to manoeuvre at the last minute onto the landing one at too low an altitude. It’s not, IMO, to stop you doing a circling approach to a non-offset runway.
There is nothing that I can think of (visual references, charted notes and ATC excepted) that stops you circling onto *any* runway off *any* approach as long as you stay within the circling area and respect the circling minima. That is the whole point of the area in the first place, yes?
To sum up generically: you can use circling minima to make an approach from any direction to any runway but you can only use IA minima for a non-offset approach. Simples!